The safety of regorafenib for the treatment of gastrointestinal stromal tumors

Introduction: The management of gastrointestinal stromal tumors (GIST) evolved due to effective molecularly targeted therapy with imatinib and sunitinib which are used first- and second-line, respectively. However, due to the development of resistance to those drugs in the majority of patients, the need for third-line therapy arose.

Areas covered: Regorafenib, an oral multitargeted inhibitor with activity against multiple kinases including KIT, RET, RAF1, BRAF, angiogenesis (VEGFR, TIE-2) and those involved in tumor microenvironment (PDGFR and FGFR) was introduced after the successful Phase III GRID (GIST – Regorafenib In progressive Disease) clinical trial. This study showed significant improvement in progression-free survival for patients receiving regorafenib compared to placebo (4.8 months vs 0.9 months). The treatment was reasonably well tolerated, with arterial hypertension, hand-foot syndrome, diarrhea being the most common grade ≥3 adverse events, which could be managed by dose reduction and supportive treatment. The aim of this paper is to describe, assess and advise on the safety of regorafenib as third-line therapy in GIST.

Expert opinion: Regorafenib has demonstrated clinical benefit in GIST patients after progression on prior treatment with at least imatinib/sunitinib and currently it is the approved standard third-line option in therapy of advanced GIST. The safety profile is similar to other multikinase inhibitors with anti-VEGFR activity and is manageable.     

Tyrosine kinase inhibitors under investigation for the treatment of type II diabetes

Introduction: Type 2 diabetes is characterized by hyperglycemia that is the result of β-cell failure in the setting of peripheral insulin resistance. It is estimated that greater than 300 million individuals worldwide have diabetes. Tyrosine kinase inhibitors (TKIs), which are used to treat a variety of cancers, appear to have antihyperglycemic effects.

Areas Covered: This review summarizes studies that have investigated the use of TKIs in animal models of diabetes. Additionally, the authors review case series describing the effects of TKIs on glucose levels in adults taking these drugs for FDA approved indications.

Expert opinion: Given the scope and size of the worldwide diabetes epidemic, reports of amelioration or possible cure of the disease warrant special attention. TKIs appear to lower glucose levels in some, but not all individuals. Multi-center prospective studies are needed in which patient with diabetes treated with TKI undergo phenotyping to identify responders versus non responders to allow for precision medicine.     

Beyond standard therapy: drugs under investigation for the treatment of gastrointestinal stromal tumor

Introduction: Gastrointestinal stromal tumor (GIST) is the most common nonepithelial malignancy of the GI tract. With the discovery of KIT and later platelet-derived growth factor α (PDGFRA) gain-of-function mutations as factors in the pathogenesis of the disease, GIST was the quintessential model for targeted therapy. Despite the successful clinical use of imatinib mesylate, a selective receptor tyrosine kinase (RTK) inhibitor that targets KIT, PDGFRA and BCR-ABL, we still do not have treatment for the long-term control of advanced GIST.

Areas covered: This review summarizes the drugs that are under investigation or have been assessed in trials for GIST treatment. The article focuses on their mechanisms of actions, the preclinical evidence of efficacy, and the clinical trials concerning safety and efficacy in humans.

Expert opinion: It is known that KIT and PDGFRA mutations in GIST patients influence the response to treatment. This observation should be taken into consideration when investigating new drugs. RECIST was developed to help uniformly report efficacy trials in oncology. Despite the usefulness of this system, many questions are being addressed about its validity in evaluating the true efficacy of drugs knowing that new targeted therapies do not affect the tumor size as much as they halt progression and prolong survival.     

Pharmacotherapy of gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GIST) are a relatively rare, but well characterised clinical entity. This tumour is defined by a predominantly spindle-cell morphology and its pathobiology by the presence of Kit (receptor tyrosine kinase). The majority of GIST have a gain of function mutation in an exon hot spot that leads to constitutive activation of Kit, promoting proliferation and anti-apoptotic signalling. Imatinib mesylate (Gleevec?, Glivec^®, Novartis) is a specific inhibitor of Kit kinase activation and in Phase II clinical trials, it has proven to be remarkably effective in heavily pre-treated patients with advanced GIST. Molecular determinants of response and resistance are the subject of ongoing investigations. Additionally, clinical trials are underway to explore the use of imatinib mesylate in the adjuvant setting. These initial evaluations with imatinib mesylate provide proof of concept for hypothesis driven, rational drug design of selective signal transduction inhibitors in the management of solid tumour malignancies.     

Emerging drugs for the treatment of gastrointestinal stromal tumour

Introduction: Tyrosine kinase inhibitors (TKIs) have transformed the treatment landscape for patients with gastrointestinal stromal tumors (GIST). Unfortunately, resistance to the currently approved TKIs poses a huge challenge, and patients are in need of additional therapeutic options. Fortunately, many novel therapeutic approaches are being tested in treatment of GIST to overcome resistance to the approved TKIs

Areas covered: We performed an extensive literature (PUBMED) search to identify emerging drugs being tested in treatment of GIST in early phase clinical trials. We discuss recent ongoing research and emerging novel inhibitors of KIT and PDGFRA receptors, inhibitors in downstream signaling pathways (mTOR and PIK3 inhibitors), inhibitors of other potential targets including ETV1/MEK, MET, FGFR, IGF1R, histone deacetylase inhibitors, heat shock protein 90 inhibitors, cyclin-dependent kinase inhibitors and immune checkpoint inhibitors in treatment of GIST

Expert opinion: Multiple agents are under evaluation; those that benefit GIST patients with imatinib resistant mutations, or those with benefit in patients refractory to approved agents are most likely to be developed in this disease. The role of immunotherapy for GIST is still investigational.     

Tyrosine kinase inhibitors to treat liver cancer

Importance of the field: Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related death worldwide. Although patients with early-stage disease have a good prognosis, there has been no effective therapy available for those with advanced disease. Despite the death risk of patients with advanced HCC being reduced with sorafenib therapy, many patients eventually turn out to be refractory to this therapy. Thus, treatment of HCC remains an urgent health concern.

Areas covered in this review: Recent improvement in understanding the pathophysiology of HCC at the molecular level has fostered the development of molecular targeted therapies that specifically block the disrupted pathways.

What the reader will gain: This review summarizes the preclinical and clinical data from 2004 to 2009 on the efficacy and safety of the emerging drug for the treatment of HCC, including small molecule inhibitors (erlotinib, sunitinib, sorafenib, vandetanib, cediranib, brivanib and dovitinib) and the rationale for combination therapies for patients with advanced HCC.

Take home message: Understanding the mechanisms of action, safety and efficacy of these new agents and new methods of combining these drugs may help prolong overall survival of patients with HCC and reduce disease recurrence after surgery or ablative therapies.     

Emerging tyrosine kinase inhibitors for the treatment of metastatic colorectal cancer

Introduction: Colorectal cancer (CRC) is a leading cause of cancer death worldwide. Over the last decade, the addition of antibodies that block the epidermal growth factor receptor (EGFR) or angiogenesis to the classic chemotherapy backbone has improved overall survival in metastatic colorectal cancer (mCRC). However, the role of the other major targeted therapy, the tyrosine kinase inhibitors (TKIs), is not yet fully clarified.

Areas covered: This review discusses key published and ongoing studies with TKIs in mCRC, the mechanisms of resistance to standard treatments that are potentially targetable with these small molecules, along with the role of biomarkers in therapeutic decision-making process.

Expert opinion: The current effectiveness of TKIs is limited by two principal reasons, firstly the use of combination chemotherapy necessitates lower dose-density to manage the toxicity profile and secondly, development of these drugs has mainly been performed in molecularly unselected populations. mCRC is a heterogeneous and dynamic disease, and clinical trials with TKIs must be designed on the basis of specific molecular alterations targeted by these drugs. Success with this approach relies on identifying mutations at the time of progression, raising the importance of minimally-invasive monitoring tools. Liquid biopsies are a promising option, although this technique remains to be validated. Overall, this approach contributes to the move towards personalized and precision therapeutic strategies.     

An overview of experimental and investigational multikinase inhibitors for the treatment of metastatic colorectal cancer

Introduction: The era of molecular-targeted agents, particularly bevacizumab and cetuximab, has revolutionized the treatment paradigm for metastatic colorectal cancer (mCRC). Amongst the multikinase inhibitors (MKIs) examined, regorafenib was the first to establish its role in mCRC. Despite its modest efficacy, this finding had reignited interest in exploring MKIs with the hope of maximizing their therapeutic potential in mCRC.

Areas covered: This review summarizes the previous studies of MKIs in mCRC, targeting two signaling pathways activated through vascular endothelial growth factor receptors and epidermal growth factor receptors. The article provides discussion with a focus on: the challenges encountered when combining MKI with chemotherapy, the lack of predictive markers, and strategies utilized to address escape pathways through combining MKIs with other targeted agents.

Expert opinion: Clinical progress using MKIs in mCRC has been disappointing due to their limited efficacy. The exact role of regorafenib, apart from in chemo-refractory disease setting, requires further delineation. The role of MKIs in combination with other targeted agents or chemotherapy and in the maintenance setting is still considered experimental and warrants further investigation. The broader role of the current generation of MKIs will depend upon the accurate identification of patients with specific molecular phenotypes and better pharmacodynamic understanding of these agents to minimize toxicity.     

Nilotinib for treatment of gastrointestinal stromal tumors: out of the equation?

Introduction: Imatinib, a selective tyrosine kinase inhibitor (TKI), is currently the standard treatment for unresectable and metastatic gastrointestinal stromal tumors (GISTs). However, the disease control time by imatinib is limited due to intolerance or resistance. Nilotinib, a second-generation TKI, is expected to show enhanced clinical efficacy against advanced GIST.

Areas covered: PubMed and ClincalTrial.gov were searched to identify clinical trials of nilotinib for GIST. The key words used were GIST and nilotinib and/or AMN107. This review summarizes the clinical trials of nilotinib for advanced GIST and outlines current understanding of the clinical usefulness of nilotinib in GIST therapy.

Expert opinion: Clinical trials of nilotinib for advanced GIST were readily advanced from a Phase I study to Phase III studies. Unfortunately, the clinical utility of nilotinib was not demonstrated by the randomized control trials either in patients with imatinib-resistant GIST or in patients who used nilotinib as the first-line treatment. On the basis of the trial results, nilotinib is not recommended for GIST therapy generally. Nevertheless, a comparable number of patients showed significant response with different side-effect profiles from imatinib. Thus, this new TKI may still merit attention as an important alternative to imatinib in advanced GIST patients who are intolerant to imatinib.     

Novel inhibitors in development for hepatocellular carcinoma

Importance of the field: The multikinase inhibitor sorafenib was the first agent to demonstrate a survival benefit for patients with locally advanced or metastatic hepatocellular carcinoma (HCC). Although sorafenib represents a landmark in the treatment of HCC and proved molecularly targeted therapy to be effective in this disease, it represents just the first step towards an improvement in systemic therapy. Since then, novel inhibitors have been evaluated in early clinical trials, showing potential activity.

Areas covered in this review: This article aims to review novel inhibitors emerging in the field of advanced HCC. An Internet-based search was performed to identify abstracts, clinical trials (www.clinicaltrials.gov, last accessed 30 November 2009), and original research and review articles.

What the reader will gain: Readers will gain a comprehensive survey of current molecularly targeted therapy approaches in advanced HCC. In addition, challenges such as the design of clinical trials, the assessment of radiological response, the role of combination therapy, and future developments in molecularly targeted therapy are discussed.

Take home message: Sorafenib is the standard of care in patients with advanced HCC. However, promising novel inhibitors are under investigation. Combined molecularly targeted therapies according to an individual genomic and proteomic profiling will probably lead to more personalised medicine in advanced HCC.     

Tyrosine kinase inhibitors as novel drugs for the treatment of diabetes

Introduction: Some inhibitors of tyrosine kinase, as imatinib, erlotinib and sunitinib have antihyperglycemic effects but the mechanisms are not totally clear.

Areas covered: It is well established that insulin resistance and beta-cell failure are hallmarks of type 2 diabetes mellitus (DM2). The present review will discuss the molecular mechanisms that account for insulin resistance and beta-cell failure in DM2, and also the effect of tyrosine kinase inhibitors in these processes.

Expert opinion: A better understanding of how these drugs improve the two most important mechanisms of DM2 associated with suggestions of clinical studies will lead to improve the treatment of this disease.     

Tyrosine kinase inhibitors in cancer treatment (Part II)

In the last few years, enormous progress in the field of signal transduction inhibition has been made. Many companies have entered the field. Along with the epidermal growth factor receptor (EGFR) tyrosine kinase, many other tyrosine kinases have been identified as interesting targets for drug discovery projects. X-ray data of more than 40 crystal structures of protein kinases, in most cases complexed with an inhibitor, have been published. Pharmacophore models for the binding of inhibitors in the ATP-binding site of protein kinases have been developed that are generally applicable, enabling the rational design of tyrosine as well as serine/threonine kinase inhibitors. It has been proven by numerous examples that the ATP-binding of protein kinases is an exciting target for the design of anticancer drugs. In many cases, it has also been demonstrated that through rational design it is possible to modify a lead structure in such a way that inhibitors with an altered selectivity profile are obtained. Chemical optimisation of several lead structures led to development candidates with potent in vitro and in vivo activity fulfilling the pharmacodynamic, pharmacokinetic, toxicological and technical (synthesis, formulation) requirements for a clinical candidate. Currently, there are seven tyrosine kinase inhibitors in early phases of clinical trials. In addition, several candidates are close to entering Phase I trials this year or at the beginning of next year. It is expected that positive results from clinical trials will greatly contribute to the clinical proof of concept of the value of signal transduction inhibition and will greatly stimulate further research in this area. This review is a continuation of a review with the same title of last year and summarises published patent literature and related publications between 1997 and September 1998.     

New molecular targets beyond KIT and PDGFRA in gastrointestinal stromal tumors: present and future

Introduction: The biological complexity of gastrointestinal stromal tumors (GISTs) and the concomitant increase in patients' life expectancy have enhanced the need for new therapeutic options to overcome the development of primary and secondary resistance to tyrosine kinase inhibitors. Aided by more sophisticated molecular biology techniques, researchers have recently sought to identify new therapeutic targets with a defined role in GISTs pathogenesis and a potential application in clinical practice.

Areas covered: The first aim of this review is to describe new targets and drugs in GISTs, alone or in combination, both in pre-clinical and clinical settings. The second aim is to discuss the criticism in this field, the role of molecular biology, and future perspectives in light of the recent development of more sophisticated whole-genomic technologies.

Expert opinion: Several targets involved in GIST pathogenesis have been identified and novel biological drugs have recently been developed, offering new treatment options in the scenario of GIST therapy. However, the identification of new therapeutic targets represents a long process and requires a global overview of the problem and a multi-step approach to convert an initial intuition or casual finding into a systematic analytical process.     

Type III or allosteric kinase inhibitors for the treatment of non-small cell lung cancer

Introduction: In recent times, there has been much interest in the development of pharmacological kinase inhibitors that treat NSCLC. Furthermore, treatment options have been guided by the development of a wide panel of synthetic small molecule kinase inhibitors. Most of the molecules developed belong to the type I class of inhibitors that target the ATP-binding site in its active conformation. The high sequence similarity in the ATP-binding site among members of the kinase families often results in low selectivity and additional toxicities. Also, second mutations in the ATP-binding site, such as threonine to methionine at position 790, have been described as a mechanism of resistance to ATP-competitive kinase inhibitors. For these reasons, alternative drug development approaches targeting sites other than the ATP cleft are being pursued. The class III or allosteric inhibitors, which bind outside the ATP-binding site, have been shown to negatively modulate kinase activity.

Areas covered: In this review, the authors discuss the most well-characterised allosteric inhibitors that have reached clinical development in NSCLC.

Expert opinion: Great progress has made in developing inhibitors with entirely new modes of action. That being said, it is important to highlight that despite their apparent simplicity, biochemical assays will remain at the core of drug discovery activities to better explore these new opportunities.     

Encorafenib in combination with binimetinib for unresectable or metastatic melanoma with BRAF mutations

Introduction: Combination treatment with a BRAF inhibitor and MEK inhibitor is the standard of care for patients with advanced BRAF^V600 mutation-positive melanoma. With the currently available combinations of dabrafenib plus trametinib and vemurafenib plus cobimetinib, median progression-free survival (PFS) of over 12 months has been achieved. However, treatment resistance and disease recurrence remain a clinical challenge.

Areas covered: Encorafenib in combination with bimetinib offers a new approach that may offer benefits over existing BRAF/MEK inhibitor combinations.

Expert opinion: While other BRAF/MEK inhibitor combinations have achieved a median overall survival (OS) of 22 months, patients with advanced BRAF mutation-positive melanoma treated with encorafenib plus binimetinib achieved a median OS of 33.6 months in the phase III COLUMBUS trial. PFS also appears to be improved with encorafenib plus binimetinib. This improved efficacy may be related to the distinct pharmacokinetics of encorafenib, with prolonged binding to the target molecule providing greater BRAF inhibition and increased potency compared with other drugs in the same class. Increased specificity of encorafenib may also result in better tolerability with less off-target effects, including reduced occurrence of pyrexia and photosensitivity. Encorafenib plus binimetinib seems likely to emerge as a valuable therapeutic alternative to established BRAF/MEK inhibitor combinations.     

Emerging tyrosine kinase inhibitors for the treatment of hepatocellular carcinoma

Introduction: Hepatocellular carcinoma (HCC) is the fifth most diagnosed cancer in the world and the third leading cause of death. Unfortunately, when diagnosed two thirds of patients have an advanced disease for which only palliative treatment can be proposed and most likely systemic therapy.

Areas covered: As of today only one systemic therapy is validated in the treatment of advanced HCC, a tyrosine kinase inhibitor (TKI): Sorafenib. Treatment options are therefore lacking. With the advent of Sorafenib other TKIs have been studied with some disappointing results. Many explanations can be found to the failure of these tested TKIs such as the underlying cirrhosis leading to rapidly serious adverse events, or trial design imperfections.

Expert opinion: Taking into account these failures, new trials with more appropriate designs have led to recent success with multi-target TKIs (Regorafenib and Lenvatinib). This multi-target approach allows to overcome the molecular heterogeneity of advanced HCC which is associated with multiple simultaneously dysregulated signaling pathways. On the contrary, another lead is to study target a specific TKI such as c-MET inhibitors or TGFβR inhibitors in HCC sub-populations with promising results in early phase trials. These results will have to be validated in the ongoing phase III trials.     

Clinical investigation of receptor and non-receptor tyrosine kinase inhibitors for the treatment of epithelial ovarian cancer

Introduction: Epithelial ovarian cancer (EOC) is the second most common gynecologic malignancy and the leading cause of death from gynecologic cancer in the USA. EOC is an exquisitely chemo-sensitive disease with response rates of over 75% in the upfront setting. Despite this, due to high rates of recurrence and development of chemo-resistance, the overall survival of EOC remains about 25%. Thus, there is a great need for new therapeutic approaches to render more durable responses. Based on preclinical and early phase clinical studies, key targeted pathways include targets that drive angiogenesis and chemo-resistance. Receptor tyrosine kinases and non-receptor tyrosine kinases play important roles in these processes and several small molecule tyrosine kinase inhibitors (TKIs) are in clinical development.

Areas covered: This review summarizes clinical rationale, mechanisms of action and clinical data for the TKIs under evaluation in the Phase III setting for EOC.

Expert opinion: Despite reasonable preclinical activity, small molecule TKIs are unlikely to improve patient survival as single agent therapies in an unselected EOC population. Incorporation of tissue evaluation during ongoing clinical trials is required to identify molecularly defined groups that respond to single agents and direct rational combination strategies based on mechanisms of resistance to improve outcomes in EOC.     

Emerging drugs for the treatment of metastatic renal cancer

For decades, options for the treatment for metastatic renal cancer have been limited and mostly ineffective. During this time, immunotherapy agents, such as IFN-α and IL-2, have represented the major treatment options. Over the last 3 years, advances in cancer biology have characterized important signaling pathways that regulate blood vessel growth and cell proliferation. These studies have identified a number of novel ‘druggable’ targets. Since 2004, this has resulted in regulatory approval of four additional agents that are active against renal cancer (bevacizumab, sorafenib, sunitinib and temsirolimus). A large number of additional candidate molecules that block the vascular endothelial growth factor and mTOR pathways have subsequently been identified. These agents are rapidly progressing through clinical testing in renal cancer and in other malignancies. This paper overviews the status of these investigational agents and anticipates areas of future research and development.     

A safety evaluation of imatinib mesylate in the treatment of gastrointestinal stromal tumor

ABSTRACT

Introduction: For the last 15 years, imatinib mesylate has been the first line treatment of choice for advanced (metastatic) GIST.

Areas covered: This review describes key efficacy data on imatinib for the treatment of GIST, and focuses on safety and tolerability of imatinib, with emphasis on common adverse events management and long term toxicity profile.

Expert opinion: Imatinib has been the standard of care for metastatic GIST and probably will continue to be so for the next few years. Still, despite dramatic responses initially, imatinib drug resistance continues to be the major factor for treatment discontinuation. The toxicity profile of imatinib has been well characterized, and although the majority of patients experience an adverse event during treatment with imatinib, these side effects are usually mild and manageable, with the majority of patients continuing treatment uninterruptedly. Early concerns regarding imatinib related cardiotoxicity in GIST have not been confirmed in large prospective randomized trials, with reports indicating a low incidence of approximately 0.2%-0.4%. Future strategies for treatment of imatinib resistant GIST will probably include novel tyrosine kinase inhibitors, combination therapies or immunotherapy.